This project investigates the expression of proto-oncogenes in the embryonic chicken lens and their relationship to cell growth, quiescence, and differentiation. The normal developmental profiles of four nuclear proto-oncogene mRNAs (c-myc, N-myc, c-fos, and c-jun) have been completed, and the study is now being extended to include the tumor suppressors, p53 and Rb, and cell-cycle regulatory proteins such as the cyclins. Functional studies have demonstrated that c- myc is involved in the transcriptional regulation of the tau-crystallin/alpha-enolase gene, and preliminary results implicate c- jun in the transcriptional regulation of alpha-crystallin. Further analysis of cell-cycle synchrony in the lens epithelium demonstrates that many synchronized cells are present in the central lens epithelium in the 14-day-old chicken embryo and that synchronized cells periodically express high levels of c-fos mRNA.